Axial Piston Machine

ABSTRACT

An axial piston machine includes two cylinder drums which are guided in a housing, can be respectively rotated about a drum axis, and are respectively supported on an inclined surface arranged in the direction of a shaft rotational axis. The inclined surfaces are located in the region between the two cylinder drums and the channels for supplying and releasing pressure end in the two inclined surfaces, i.e. pressure is supplied and released centrally.

The invention relates to an axial piston machine in accordance with thepreamble of claim 1.

Axial piston machines of this type known, for instance, from WO03/058034 A1 comprise two cylinder drums in each of which a plurality ofcylinders is formed. A shaft which is fixedly connected to a pluralityof pistons confining a respective pressure chamber by the cylinders ofthe cylinder drums passes through the two cylinder drums. The cylinderdrums are supported on inclined surfaces the inclination of which isselected such that the axis of rotation of the cylinder drums isinclined with respect to the shaft axis. The inclined surfacessupporting the cylinder drums do not rotate together with the shaft orthe cylinder drum so that the pistons pass an elliptic track of motionwith respect to the plane of the inclined surfaces supporting thecylinder drums. In the known solutions the cylinder drums are locatedwith the pistons between the two inclined surfaces, the latter beingrespectively formed on control disks which are supported on the housingof the axial piston pump and via which pressure is supplied andreleased.

When testing the known axial piston machines it turned out that inoperation of the axial piston machine the noise emission is relativelyhigh so that insulating measures have to be provided. It is anotherdrawback of the known solutions that the pressure supply via the twoexternal control disks requires a comparatively complex design of thepressure and tank channels.

Compared to this, the object underlying the invention is to provide anaxial piston machine having a comparatively simple design in which thenoise emission is reduced vis-à-vis conventional solutions.

This object is achieved by an axial piston machine comprising thefeatures of claim 1.

In accordance with the invention, two cylinder drums of the axial pistonmachine are formed on respective inclined surfaces, wherein saidinclined surfaces are arranged centrally, i.e. in the area between thetwo cylinder drums, and a pressure channel and a tank channel end insaid inclined surfaces. By way of this central arrangement of theinclined surfaces the ducting can be considerably facilitated comparedto the conventional solutions so that the costs of manufacturing theaxial piston machine are comparatively low. It is another advantage thatby the central arrangement the forces of pressure acting on the twoinclined surfaces are substantially mutually neutralized so that thepressure forces introduced into the housing via the inclined surfacesare very small and, accordingly, also the noise emission is reducedwhich, in conventional solutions, can adopt an unacceptable degree bythe forces introduced via the external control disks into the housinghaving large noise-radiating surfaces.

In the case of an especially compact variant the two end faces areformed on a control disk which is centrally inserted in the housing andthrough which a shaft supporting the pistons passes.

For further reducing the noise emission an insulating layer can beprovided between the control disk and the housing. In such an embodimentit is preferred when the control disk includes a protection againsttorsional twist in the form of a flattened portion, for instance.

In order to prevent a relative twisting of the resiliently supportedcontrol disk inside the housing, it is preferred in this solution toarrange and design the central pressure ports such that the forcesacting via the pressure ports, especially the pressure port on thecontrol disk, are so great that the torques transmitted by rotation ofthe cylinder drum to the control disk are substantially compensated.

In the case that the axial piston machine is to be operated as pump orhydraulic motor the control disk has two kidney-shaped control membersone of which is allocated to a pressure port and the other is allocatedto a tank port. In a variant of the invention it is preferred when thechannels connected to the pressure and tank ports tangentially end inthe kidney-shaped control members.

The axial piston machine can be basically operated as hydraulictransformer as well. However, this requires that the control disk isrotatably accommodated in the housing and that it includes threekidney-shaped control members.

Other advantageous further developments of the invention are the subjectmatter of further subclaims.

Hereinafter preferred embodiments of the invention will be illustratedby way of schematic drawings in which:

FIG. 1 shows a schematic longitudinal section across a first embodimentof an axial piston machine;

FIG. 2 shows a simplified sectional representation of the axial pistonmachine from FIG. 1;

FIG. 3 shows an enlarged detailed representation of the axial pistonmachine from FIG. 1 and

FIGS. 4, 5 are representations of a second embodiment of an axial pistonmachine corresponding to the FIGS. 1 and 2.

In FIG. 1 a simplified longitudinal section across a first embodiment ofan axial piston machine 1, for instance a hydraulic pump, is shown. FIG.2 illustrates a section, which is geometrically not exact, along thedot-dash vertical line y in FIG. 1. Accordingly, the axial pistonmachine 1 has a housing 2 in which a shaft bore 4 is formed. In thelatter a shaft 6 is supported by two shaft bearings 8, 10. Said shaft 6(drive shaft in a pump) supports two cylinder drums 12, 14 therotational axes Z1 and Z2 of which are inclined with respect to therotational axis X of the shaft 6.

The two cylinder drums 12, 14 inclined with respect to each other aresupported on a control disk 16 accommodated centrally (view according toFIG. 1) in the housing 2. The end faces of said control disk 16 areformed by two inclined surfaces 18, 20. According to FIG. 1, theseinclined surfaces 18, 20 are inclined with respect to each other in suchmanner that the control disk 16 is tapered downwards from the radiallyupper portion of the housing 2.

Each cylinder drum 12, 14 has a plurality of cylinders 22 and 24,respectively, in each of which a piston 26, 28 immerses. The pistons 26and 28, resp., allocated to the cylinder drums 12, 14 are arrangedaxially in parallel to the shaft axis X and are mounted on a flange 30,32 which is formed integrally with the shaft 6 or is mounted on thesame. The pistons 26, 28 confine by the cylinders 22, 24 a respectivepressure chamber 34, 36 which is adapted to be connected—as described indetail hereinafter—to a pressure port P or a tank port T. In thesectional representation of FIG. 2 the two ports T, P are arranged atthe cylinder housing 2 in the central plane including the central axisY. The two ports P, T are connected to a respective kidney-shapedcontrol member (tank control member 42 and pressure control member 44)via a tank channel 38 and a pressure channel 40, respectively. Inaccordance with FIG. 2, the two channels 38, 40 tangentially end in theallocated kidney-shaped control member 42 and 44, respectively. Thelatter encompass the shaft 6 in portions so that a respective land 46,48 of the control disk 16 remains between the end portions thereofarranged at the top in FIG. 2 and the end portions thereof arranged atthe bottom in FIG. 2. The two control members 42, 44 end in therespective two inclined surfaces 18, 20.

As one can take especially from FIG. 1, the axial piston machine 1 has asymmetric design with respect to the Y axis, wherein the control disk 16is centrally arranged at the inclined surfaces 18, 20 of which the twocylinder drums 12, 14 are supported. Said cylinder drums interact withthe pistons 26, 28 which are fixedly connected to the shaft 6 via theflange 30 and 32, respectively.

Since the structure of the two cylinder drums 12, 14 is identical,constructional details will be illustrated by way of the enlargedrepresentation according to FIG. 3 showing the cylinder drum 14.Accordingly, the latter has a drum plate 50 which is slidingly supportedon the inclined surface 20 of the control disk 16 by its end face 52shown on the left in FIG. 3. The drum plate 50 has a mounting hub 54which is supported on a domed, i.e. convexly curved bearing portion 59of the shaft 6 by a self-aligning bearing 56 or the like. Thisself-aligning bearing 56 permits an inclination of the axis Z2 of therotational axis of the cylinder drum 14 vis-à-vis the shaft axis X. Anannular drum body 60 on which the cylinders 24 of the cylinder drum 14are formed is supported on an annular end face 58 of the drum plate 50which is internally confined by the mounting hub 54. Said drum body 60can be composed of a plurality of individual elements. In the solutionknown from WO 03/058034 A1 this drum body 60 is formed of a plurality ofcylinder sleeves, for instance, which are interconnected by a holdingring. The cylinder sleeves can also be supported on the drum plate 50via spring bias and a joint. Basically the drum body 60 can also beintegrally formed.

As indicated in FIG. 3, the drum body 60 or the individual elementsthereof forming the cylinder 24 are not in full-surface contact with theannular end face 58 but are only in contact by a contacting portionformed by a projection 62.

As mentioned in the foregoing, in the drum body 60 a plurality ofcylinders 24 is formed in which the end portions of the pistons 28immerse so that respective pressure chambers 24, 36 are confined by thecylinders 24 and the pistons 28. The pressure chamber 36 located at thebottom in FIG. 3 has the maximum volume (piston provided in its outerdead-center position), while in the relative position between the piston28 and the cylinder 24 shown at the top of FIG. 3 the pressure chamber36 has its minimum volume (piston provided in its inner dead-centerposition).

Pressure is supplied to said pressure chambers 36 of the cylinders 24via sockets 62 passing through the bottom of the cylinder chambers 24and being slidingly supported on the inner end face of the respectivecylinder 24 of the drum body 60 by a radial projection 64. The endportion of the socket 62 distant from the radial projection 64 isinserted in an appropriately designed seat 66 of the drum plate 50. Aconnecting channel 68 adapted to be connected to the kidney-shapedpressure control member 44 or tank control member 42 depending on therotary position of the cylinder drum 14 ends in this seat 66.

Each piston 28 includes a mounting portion 70 via which it is supportedin the flange 32 of the shaft 6. Subsequent to the mounting portion 70the piston 28 is radially set back and is transformed into a taperedportion 72 by which the piston 28 is extended up to its maximumcross-section. Said maximum cross-section is provided with the referencenumeral 74 in FIG. 3. Subsequent to said maximum cross-section 74 thepiston is somewhat tapered again. This tapered shape of the pistons 28is necessary so that they do not collide with the cylinder walls in theinner dead-center position (top of FIG. 3). In accordance with FIG. 3,the pistons are adjacent to the inner circumferential surfaces of thecylinders 24 along their maximum cross-section. For improving the seal arespective piston ring may be provided at the outer circumference of thepistons 28 in this contacting area.

When driving the shaft 6 the pistons 26, 28 rotate about the shaft axisX, whereas the two cylinder drums 12, 14 rotate about their axis Z1 andZ2, respectively. During this movement of rotation the cylinder drumsare supported on the central control disk 16. By the inclination of thecylinder drums 12, 14 the pressure chamber located at the top in FIG. 3is enlarged upon further rotation (suction), while the lower pressurechamber 36 is reduced (pressure build-up). The control disk 16 isarranged so that the kidney-shaped tank member 42 is connected to theenlarging pressure chambers and the pressure control member 44 isconnected to the reducing pressure chambers. In the area of thedead-center positions (FIG. 3) the connection to the two ports P, T isblocked by the lands 46, 48 so that a change-over between pressure portand tank port and vice versa can be carried out.

Due to the inclination of the cylinder drums 12, 14 the pistons 26, 28pass an elliptic orbit with respect to the allocated inclined surfaces18, 20. The drum body 60 is designed such that the elements forming thecylinders can slightly slide off along the annular end face 58 so as tocompensate for these relative movements.

The essential difference between the solution according to the inventionand the known solutions described in the beginning is that pressure issupplied centrally via the control disk 16 and that by the symmetriccentral design of the control disk 16 the pressure forces transmitted bythe two cylinder drums 12, 14 are largely neutralized. The pressureforces acting on the pistons 26, 28 are introduced to the shaft 6 viathe flanges 30, 32, i.e. the pressure forces are not guided via thehousing including its large noise-radiating surfaces. It is anothersubstantial advantage of the invention that the pressure fluid channelscan be arranged very simply and spaced very closely by the centrallylocated ports so that the structure of the axial piston machine issubstantially facilitated vis-à-vis the known solutions.

The noise radiation during operation of the axial piston machine can befurther improved by the embodiment illustrated by way of the FIGS. 4 and5.

The embodiment shown in FIGS. 4 and 5 substantially differs from theafore-described embodiment merely by the design of the control disk 16and the ducting in the control disk 16. The structure of the cylinderdrum 12, 14 and the shaft 6 is identical to the above-describedembodiment so that hereinafter only the differences will be discussed.

In the embodiment shown in FIGS. 4 and 5 the control disk 16 is neithermounted directly in the housing 2 nor is it formed integrally with thesame, but it is a separate component part, wherein in the mounted statean insulating layer is formed between the housing 2 and the control disk16. Said layer can be made, for instance, of elastic synthetic materialhaving sound-insulating characteristics. For protecting the control disk16 against twisting it is provided with a flattened portion 78; a recess80 of the housing 2 is appropriately designed. The elastic insulatinglayer 76 is inserted in said recess 80 and encompasses the outercircumference of the control disk 16. By decoupling the control disk 16from the housing 2 the noise emissions can be further reduced, to besure, in the case of unfavorable operating conditions, however, arelative twist can occur between the control disk 16 and the housing 2despite the flattened portion due to the elasticity of the insulatinglayer 76. In order to prevent this, the ports T, P are located such thatthe pressure forces acting on the control disk 16 via the two ports T, P(especially P) can compensate for this torque. I.e. the axial distance aand the cross-sectional area of the pressure channel 40 are selected,for instance, such that the pressure force FH transmitted via thepressure fluid at the control port P to the control disk 16 generates atorque (FH×a) which compensates for the radial force acting on thecontrol disk 16 during operation and the torque resulting therefrom. Ofcourse, also other measures for supporting the torque can be provided.

An axial piston machine is disclosed comprising two cylinder drums whichare guided in a housing, can be respectively rotated about a drum axisand are respectively supported on an inclined surface arranged in thedirection of a shaft rotational axis. In accordance with the invention,said inclined surfaces are located in the region between the twocylinder drums and the channels for supplying and releasing pressure endin said two inclined surfaces, i.e. pressure is supplied and releasedcentrally.

LIST OF REFERENCE NUMERALS

-   1 Axial piston machine-   2 housing-   4 shaft bore-   6 shaft-   8 shaft bearing-   10 shaft bearing-   12 cylinder drum-   14 cylinder drum-   16 control disk-   18 inclined surface-   20 inclined surface-   22 cylinder-   24 cylinder-   26 piston-   28 piston-   30 flange-   32 flange-   34 pressure chamber-   36 pressure chamber-   38 tank channel-   40 pressure channel-   42 kidney-shaped tank control member-   44 kidney-shaped pressure control member-   46 land-   48 land-   50 drum plate-   52 end face-   54 mounting hub-   56 self-aligning axis-   58 annular end face-   59 bearing portion-   60 drum body-   62 socket-   64 radial projection-   66 seat-   68 connecting channel-   70 mounting portion-   72 tapered portion-   74 maximum cross-section-   76 insulating layer-   78 flattened portion-   80 seat

1. An axial piston machine comprising two cylinder drums which areguided in a housing, can be respectively rotated about a drum axis andare respectively supported on an inclined surface, wherein pistons whichcan be rotated about a shaft axis inclined with respect to the drum axesare allocated to each cylinder drum, wherein pressure chambers adaptedto be connected to a pressure port and a tank port, respectively, of thehousing via pressure and tank channels are confined by cylinders of thecylinder drums and the pistons characterized in that the inclinedsurfaces are arranged in the region between the two cylinder drums andthat the channels end in the inclined surfaces.
 2. An axial pistonmachine according to claim 1, wherein the inclined surfaces are formedon end faces of a control disk through which a drive shaft or outputshaft passes.
 3. An axial piston machine according to claim 2, whereinan insulating layer is formed between the control disk and the housing.4. An axial piston machine according to claim 2, wherein the controldisk has a flattened portion as a protection against torsional twist. 5.An axial piston machine according to claim 4, wherein an axial distanceof a central axis of the pressure port and the cross-sectional area ofthe pressure channel are selected in the transient portion between thehousing and the control disk such that the radial force acting on thecontrol disk and the torque resulting therefrom can be compensated forby the forces of pressure acting via the pressure port on the controldisk.
 6. An axial piston machine according to claim 1, wherein thecontrol disk includes control members located on a joint referencecircle in which the pressure and tank ports end.
 7. An axial pistonmachine according to claim 1, wherein it is operated as hydraulic pumpor as hydraulic motor.